Invertible filter centrifuges are known (DE 43 16 081 C1), with which a mechanical dehumidification and drying of the filter cake adhering to the drum wall takes place in the rotating centrifugal drum and the filter cake has drying gas flowing through it for additional dehumidification, wherein the efficiency of the dehumidification and drying naturally depends on the temperature and velocity of the gas flowing through. It is also known in the case of such invertible filter centrifuges for the capillaries of the filter cake to be blown free with a gas subject to a relatively high pressure, prior to the drying gas flowing through the filter cake, in order to thus open a path for the drying gas.
In addition, it is known, in those cases in which the dehumidification and drying in the invertible filter centrifuge are not sufficient, to provide thermal units downstream of the centrifuge in the form of a solids dryer, in which the solids withdrawn from the invertible filter centrifuge are treated by means of heat contact by way of heating and/or by means of heat convection with the aid of a flow of drying gas, in order to bring about a further dehumidification and drying of the solids until the desired final value is reached. In many cases it is also necessary to bring about the required final degree of drying (residual moisture) by means of a final drying in a vacuum. A deagglomeration of the solids by means of alternating application of a vacuum and pressure is also possible. As a rule, the final drying or deagglomeration takes place in a vacuum in the solids dryer although these processes can also, in principle, be carried out in the invertible filter centrifuge.
Air or another, in particular, an inert gas are considered as drying gas. If the drying gas is contaminated with toxic agents during the dehumidification and drying process not only in the invertible filter centrifuge but also in the solids dryer, it must be either disposed of or treated in a processing plant so that the cleaned drying gas can be used again in the cycle for the dehumidification and drying in the invertible filter centrifuge and in the solids dryer and the consumption of inlet gas is reduced to a minimum.
When the solids predried in the invertible filter centrifuge are transferred into the solids dryer, larger solids agglomerates, which can result due to too great a compression or capillary binding forces which are too high, often make themselves interferingly noticeable. In this case, a deagglomeration, i.e. a reduction in size, must be carried out prior to the solids entering the solids dryer.
During conventional operation of invertible filter centrifuges and solids dryers, these are decoupled, i.e. each of these units is dimensioned and controlled separately with respect to the result to be attained for a certain product. In this respect, in the concrete case of use the size of each unit must be adjusted according to the worst results which might occur and are to be taken into account, wherein the resting time in the invertible filter centrifuge or in the solids dryer can be too long, for example, due to error batches which have to be included in calculations.
Since, in the case of known systems, neither the dehumidification and drying in the invertible filter centrifuge nor the dehumidification and drying in the solids dryer can be coordinated with one another in their results, the units consisting of invertible filter centrifuge and solids dryer often work uneconomically as a result of maintenance or stoppage times. Also, such units are often designed with too high a safety level with respect to fulfilling specific production expectations which directly influences the manufacturing costs of the units and their operating costs negatively.
The degree of dehumidification which can be achieved in the invertible filter centrifuge by mechanical centrifugation can also be limited and so, for example, as a result of a thixotropic behavior of the separated solids these can adhere to or "cake on" undesired locations and make further transport of the product into the solids dryer more difficult. This may also result in undesired stoppage times. Moreover, additional equipment may be necessary which likewise drives up the cost of required investments.
The object of the invention is to further develop a generic invertible filter centrifuge with a post-connected solids dryer such that invertible filter centrifuge and solids dryer complement one another synergetically during operation in order to achieve a specific degree of dehumidification, wherein the use of the thermal energy of the drying gas is intended, in particular, to be optimized.
This object is accomplished by claim 1.